1. Field of the Invention
The present invention relates generally to a method and apparatus for monitoring the die penetration depth of a mechanical press. Specifically, the present invention relates to a method and apparatus for monitoring die penetration depth which indirectly measures die penetration depth.
2. Description of the Related Art
Mechanical presses of the type performing stamping and drawing operations employ a conventional construction which includes a frame structure having a crown and a bed and which supports a slide in a manner enabling reciprocating movement toward and away from the bed. These press machines are widely used for a variety of workpiece operations and employ a large selection of die sets with the press machine varying considerably in size and available tonnage depending upon its intended use.
Conventional press machines employ a tooling apparatus in the form of a die assembly to shape a workpiece, such as in a stamping or drawing operation. The die assembly particularly includes a lower die attached to the bed or bolster and an upper die or punch attached to the slide. The upper and lower dies are installed in opposing spaced apart relation to one another and cooperate during press machine operation to mutually engage the workpiece at respective sides thereof to thereby effect the desired forming activity.
Repeated stamping operations of a mechanical press cause die wear. The ability to accurately predict die wear and/or to predict operating conditions which indicate the propensity for increased die wear is advantageous in that press down time for die replacement or reconditioning can be predicted or potentially diverted by proactive early corrective intervention. During press operation, the upper die or punch may continue to penetrate into the lower die after effecting the desired forming activity on the stock material. This continued punch penetration into the lower die contributes to punch or upper die wear. Minimizing die penetration depth will lead to increased die longevity. Minimizing die penetration depth additionally decreases the chance that the upper die or punch will chip or deform.
Upper die or punch penetration into the lower die additionally leads to increased punch wear since upper die penetration leads to additional punch surface area coming into contact with and being worn by stock material. This additional punch penetration leads to additional punch surface area which must be reground when the die is serviced. Having to resurface additional area of the punch is not only time consuming but leads to decreased punch longevity since additional material must be ground away from the punch.
What is needed in the art is a method and apparatus to monitor die penetration depth so that die penetration depth may be minimized and consequently tooling lifetime and maintenance intervals may be more accurately predicted.
The present invention provides a method and apparatus for monitoring die penetration without requiring a direct measurement thereof. Specifically, the method and apparatus of the present invention utilizes measured quantities such as the contact point where the slide contacts the stock material, the dynamic die bottom dead center point of the slide under a load condition, and stock material thickness to compute a measure of die penetration. Dynamic die bottom dead center is defined as the point furthest from top dead center reached by the die being monitored. The method and apparatus of the current invention additionally creates a database of monitored die penetration, die number, actual running speed of the press, and material specifications including material hardness so that optimum operating conditions of a mechanical press leading to minimum die penetration depth may be determined.
The invention, in one form thereof, comprises a method of monitoring performance parameters for a mechanical press. This method includes the steps of: determining the distance between the contact point and the dynamic die bottom dead center point of the slide during a load condition of the press, determining the stock material thickness, and subtracting the stock material thickness from the determined distance between the contact point and the dynamic die bottom dead center point of the slide to calculate die penetration depth. This method may further include the steps of: providing a computational device, communicating the contact point and the dynamic die bottom dead center point of the slide during a load condition of the press to the computational device, using the computational device to determine the distance between the contact point and the dynamic die bottom dead center point, communicating the stock material thickness to the computational device, and using the computational device to subtract the stock material thickness from the distance between the contact point and the dynamic die bottom dead center point of the slide to determine the die penetration depth.
The step of determining the distance between the contact point and the dynamic die bottom dead center point of the slide during a load condition of the press is achieved in one form of the current invention by generating an actual slide displacement curve during a load condition of the press, determining the contact point on the actual slide displacement curve which corresponds to the slide contacting the stock material, determining the dynamic die bottom dead center point on the actual slide displacement curve, and measuring the distance along the slide path between the contact point and the dynamic die bottom dead center point.
In one form of the current invention, the step of generating an actual slide displacement curve during a load condition of the press is accomplished by monitoring the displacement of the slide of the press and plotting slide displacement vs. a count quantity. The step of plotting slide displacement vs. a count quantity may be accomplished by plotting slide displacement vs. crank angle or by plotting slide displacement vs. time.
In one form of the current invention, the step of determining the contact point on the actual slide displacement curve includes the steps of: determining the first inflection point on the actual slide displacement curve and establishing the contact point on the actual slide displacement curve as the first inflection point on the actual slide displacement curve.
In one form of the current invention, the step of determining the dynamic die bottom dead center point on the actual slide displacement curve includes the steps of: determining the top dead center location of the slide, determining the point on the actual slide displacement curve that is at the greatest distance along the slide path from the top dead center location of the slide, and establishing the dynamic die bottom dead center point on the actual slide displacement curve as the point on the actual slide displacement curve that is at the greatest distance along the slide path from the top dead center location of the slide.
The invention, in another form thereof, comprises a method of monitoring performance parameters for a mechanical press. This method includes the steps of: determining the distance between the contact point and the dynamic die bottom dead center point of the slide during a load condition of the press, determining the stock material thickness, subtracting the stock material thickness from the distance between the contact point and the dynamic die bottom dead center point of the slide to determine the die penetration depth, providing a computer storage device, and inputting variables corresponding to press operational parameters into the computer storage device. The step of inputting variables corresponding to press operational parameters may further include the steps of: inputting a value of die number for the press being monitored, inputting a value of press speed for the press being monitored, inputting values corresponding to the material specifications of the stock material, and inputting computed values of die penetration depth. The step of inputting values corresponding to the material specifications of the stock material may comprise inputting a value of material hardness of the stock material.
The invention, in another form thereof, comprises a method of monitoring performance parameters for a mechanical press. This method includes the steps of: determining the distance between the contact point and the dynamic die bottom dead center point of the slide during a load condition of the press, determining the stock material thickness, subtracting the stock material thickness from the distance between the contact point and the dynamic die bottom dead center point of the slide to determine the die penetration depth, providing a computer storage device, inputting variables corresponding to press operational parameters into the computer storage device, constructing a database of press operational parameters including die penetration values, and determining optimum minimum die penetration conditions for the press being monitored. In one form of the current invention, this method further includes the step of: adjusting the shutheight of the press being monitored in response to the die penetration being experienced by the press being monitored so as to minimize die penetration.
The invention, in another form thereof, comprises a method of monitoring performance parameters for a mechanical press.
This method includes the steps of: determining the location of the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide, determining the location of the dynamic die bottom dead center point of the slide during a load condition of the press, and determining the distance along the slide path between the dynamic die bottom dead center point of the slide during a load condition of the press and the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide to determine die penetration depth. In one form of the current invention, this method further includes the steps of: providing a computational device, communicating the location of the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide to the computational device, communicating the location of the dynamic die bottom dead center point of the slide during a load condition of the press to the computational device, and using the computational device to determine the distance along the slide path between the dynamic die bottom dead center point of the slide during a load condition of the press and the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide to determine die penetration depth.
The invention, in another form thereof, comprises a method of monitoring performance parameters for a mechanical press. This method includes the steps of: determining the location of the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide, determining the location of the dynamic die bottom dead center point of the slide during a load condition of the press, and determining the distance along the slide path between the dynamic die bottom dead center point of the slide during a load condition of the press and the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide to determine die penetration depth. In one form of the current invention, the step of determining the location of the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide includes the steps of: choosing a reference point, determining the contact point height relative to the chosen reference point, determining the stock material thickness, and subtracting the stock material thickness from the contact point height to determine the height of the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide relative to the chosen reference point.
In one form of the current invention, the step of determining the contact point height relative to the chosen reference point includes the steps of: generating an actual slide displacement curve during a load condition of the press; determining the first inflection point on the actual slide displacement curve; establishing the contact point on the actual slide displacement curve as the first inflection point on the actual slide displacement curve; and determining the distance, along the slide path, between the contact point and the chosen reference point.
In one form of the current invention, the step of determining the location of the dynamic die bottom dead center point of the slide during a load condition of the press comprises determining the dynamic die bottom dead center point height relative to the chosen reference point. The step of determining the dynamic die bottom dead center point height relative to the chosen reference point may further includes the steps of: determining the top dead center location of the slide; determining the point on the actual slide displacement curve that is at the greatest distance from the top dead center location of the slide; establishing the dynamic die bottom dead center point on the actual slide displacement curve as the point on the actual slide displacement curve that is at the greatest distance from the top dead center location of the slide; and determining the distance, along the slide path, between the dynamic die bottom dead center point and the chosen reference point.
In one form of the current invention, the step of determining the distance along the slide path between the dynamic die bottom dead center point of the slide during a load condition of the press and the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide to determine die penetration depth includes the step of: determining the distance between the height of the stock material surface which is the greatest distance along the slide path from the top dead center position of the slide and the height of the dynamic die bottom dead center point to determine the die penetration depth.
The invention, in another form thereof, comprises an apparatus for monitoring a running press. The apparatus of this form of the current invention includes an input means for inputting a plurality of input values, which include a value of material thickness corresponding to the stock material being utilized. The apparatus of this form of the current invention further includes a computational device for computing a plurality of computed values including a measure of die penetration depth. The input means are communicatively connected to the computational device so that input values may be utilized in the computational device. A non-contact displacement sensor is utilized to sense slide displacement during an actual load condition of the press. The non-contact displacement sensor is communicatively connected to the computational device so that the computational device is operable to plot sensed slide displacement vs. a count quantity. Slide displacement vs. count quantity is plotted to generate an actual slide displacement curve. The count quantity can be a measure of time or crank angle. The computational device is operable to determine the contact point on the actual slide displacement curve which contact point corresponds to the slide contacting the stock material. The computational device additionally determines the dynamic die bottom dead center point on the actual slide displacement curve. The computational device utilizes the contact point, the dynamic die bottom dead center point, and the stock material thickness to compute a value of die penetration depth. The computational device can be, for example, a microprocessor.
The plurality of input values input via the input means can include a value corresponding to the die number for the press being monitored and a plurality of values corresponding to the specifications of the stock material being utilized in the press, including a value of stock material hardness.
A speed sensor may additionally be utilized to sense a value of press operational speed. The speed sensor is communicatively connected to the computational device. In one form of the current invention, a computer storage device is communicatively connected to the computational device and is operative to store the plurality of computed values, the plurality of input values, and the monitored value of press speed. The computer storage device is operable to create a database of the input and computed values, as well as the value of press speed.
The invention, in another form thereof, comprises a method of monitoring performance parameters for a mechanical press. This method includes the steps of: generating a theoretical no-load slide displacement curve for the press, determining the theoretical contact point on the theoretical no-load slide displacement curve, determining the theoretical bottom dead center point on the theoretical no-load slide displacement curve, determining the distance between the theoretical contact point and the theoretical bottom dead center point, determining the stock material thickness, and subtracting the stock material thickness from said distance.
In one embodiment, the step of determining the theoretical contact point on the theoretical no-load slide displacement curve comprises: generating an actual slide displacement curve during a load condition of the press, determining the contact point on the actual slide displacement curve which corresponds to the slide contacting the stock material, superimposing the theoretical no-load slide displacement curve and the actual slide displacement curve, determining the contact point on the actual slide displacement curve, determining the point on the downstroke of the theoretical no-load slide displacement curve which maintains the same location along the ordinate as the contact point, and establishing the point on the downstroke of the theoretical no-load slide displacement curve corresponding to the actual contact point as the theoretical contact point.
An advantage of the present invention is the ability to monitor die penetration depth without directly measuring die penetration depth.
Another advantage of the present invention is the ability to monitor die penetration depth utilizing a slide displacement curve which slide displacement curve may additionally be utilized to determine various other press operational parameters.
Yet another advantage of the present invention is the ability to minimize die penetration and therefore minimize punch chipping.
A further advantage of the present invention is the ability to monitor tooling performance and predict and schedule tooling maintenance, e.g. punch sharpening.
Yet another advantage of the present invention is the ability to predict press operational characteristics which will minimize die penetration depth.
Yet another advantage of the present invention is the ability to minimize punch surface area that contacts the stock material and to consequently decrease punch wear.